Epithelial surfaces form the first line of defense against microbes. A small proportion of incoming microbes that enter at sites of microlesions is handled by antigen-presenting cells (APCs), which are mostly dendritic cells (DC) (Steinman, 1991).
Candida albicans is among the most frequently isolated fungal pathogen in humans that invade the mucosal surface (Edwards, 1991). As the major cause of hospital-acquired fungal infections (Sternberg, 1994), the recognition of C. albicans by cell surface receptors has major pathogenetic consequences. Nevertheless, only limited information is available on the molecular mechanisms involved in recognition of this fungus. C. albicans can switch from a unicellular yeast form into various filamentous forms, all of which can be found in infected tissues (Odds, 1987). The ability to reversibly switch between these forms is thought to be important for Candida's virulence. Several studies now demonstrate that dendritic cells can bind and phagocytose fungi like Candida albicans (d'Ostiani et al., 2000; Forsyth et al., 1998; Huang et al., 2001). Reports have indicated that protection from mucocutaneous candidiasis relies on cell-mediated immunity induced after processing of Candida and presentation by DC to prime T cells (Newman and Holly, 2001).
Recent studies in mice demonstrate that while the yeast form activates dendritic cells for IL-12 production and priming of T helper type 1 (Th1) cells, the hyphal form inhibits IL-12 and Th1 priming and induces IL-4 production (d'Ostiani et al., 2000). These results indicate that dendritic cells fulfill the requirement of a cell uniquely capable of sensing the two forms of C. albicans (d'Ostiani et al., 2000). In addition, it was recently reported that human dendritic cells are also able to bind C. albicans, and that this interaction is mediated by the mannose -fucose receptor (FR, CD206), as observed also on macrophages (Newman and Holly, 2001).
Both the yeast form and the hyphae form of yeast are phagocytosed by dendritic cells (d'Ostiani et al, 2000). But each form is treated differently by the cells and results in a different response. Phagocytosis of the yeast form activates dendritic cells for interleukin-12 production and priming of T helper type 1 (Th1) cells thereby aiding in mounting an immune response. In contrast, phagocytosis of the hyphal form inhibited IL-12 production and Th1 priming and induced IL-4 production which suppresses the immune response and favors Th2 cells. Whereas Th1 cells mediate phagocyte-dependent protection and are the principal mediators of acquired protective immunity, Th2-like reactivity is frequently observed in patients with Candida-related pathology (d'Ostiani et al., 2000).
There is also evidence that the type of response depends upon the receptor used to take up the pathogenic organism. Candida yeast uptake is more sensitive to mannan inhibition than is uptake of the Candida hyphae. This suggested that receptors in addition to the mannose receptor are involved in uptake of Candida (d'Ostiani et al., 2000). Receptors for antigen capture on dendritic and phagocytic cells vary in their ligand and specificity and mode of delivery to antigen-processing compartments (d'Ostiani et al., 2000; Aderem and Underhill, 1999; Vidarsson and van de Winkel, 1998; Mosser and Karp, 1999). The mannose receptor-mediated phagocytosis of nonopsonized C. albicans resulted in the generation of proinflammatory cytokines (Yamamoto et al, 1997), and the mannose receptor-mediated phagocytosis of zymosan initiated IL-12 production in phagocytes (Shibata et al, 1997). In contrast, interaction with receptors other than the mannose receptors, including CR3 (Forsyth et al, 1998), led to suppression of the immune response to C. albicans (Szabo et al., 1995) and other fungi (Marth and Kelsall, 1997).
Recently, a novel C-type lectin, designated DC-specific ICAM-grabbing non-integrin (DC-SIGN; CD209) was isolated from monocyte-derived dendritic cells (Geijtenbeek et al., 2000a). It was discovered that besides the capacity of DC-SIGN to bind and capture HIV-1 at mucosal sites of initial infection and protecting the virus from degradation for subsequent transport by DC to lymphoid organs (Geijtenbeek et al., 2000b), DC-SIGN acts as a binding partner for ICAM-3 (Geijtenbeek et al., 2000a). This early contact may enable the T cell receptor (TCR) to scan for processed antigens, allowing the initiation of primary immune responses. DC-SIGN also displays a high affinity for ICAM-2, supporting transendothelial migration of DC and DC trafficking (Geijtenbeek et al., 2000c).
Naive T cells are characterized by a high expression of ICAM-3 which is a member of the IgG supergene family and is rapidly downregulated after activation (Vazeux et al., 1992). It was observed that DC-SIGN mediates adhesion between dendritic cells and ICAM-3 on naive T cells and appears to be essential for DC-induced T cell proliferation (Geijtenbeek et al., 2000a; Steinman, 2000).
Modulation of immune responses can be achieved by affecting the interaction between dendritic cells and T cells (see WO 00/63251, the contents of which are specifically incorporated herein by reference in their entirety, which describes the finding of DC-SIGN on dendritic cells in healthy persons). Immune responses can be inhibited or prevented by preventing the interaction of DC-SIGN on dendritic cells with receptors on T cells, e.g., by using antibodies specific for DC-SIGN. Alternatively, an immune response to an antigen can be potentiated by binding the antigen to DC-SIGN on dendritic cells such that the antigen plus DC-SIGN is taken up by dendritic cells and processed and presented to T cells.
WO 96/23882 describes a murine and human receptor with C-type lectin domains that is abundantly expressed on the surface of dendritic cells and thymic epithelial cells. The murine receptor—named “DEC-205”—is described as a 205 kDa protein with an isoelectric point of about 7.5 that contains 10 C-type lectin domains and that is homologous to the macrophage mannose receptor (MMR).
WO 96/23882 further describes monoclonal and polyclonal antibodies against DEC-205. However, these antibodies were not able to block dendritic cell function. In particular, monoclonal and polyclonal anti-DEC-205 antibodies were unable to inhibit the interaction between dendritic cells and helper T cells, both in vitro (as determined by the inability of anti-DEC-205 to inhibit allogenic T cell proliferation in a one way mixed leukocyte reaction) and in vivo (as determined by the inability of anti-DEC-205 to inhibit an in vivo response, i.e. in a local graft-versus-host (GVH) reaction). These results suggest that the DEC-205 receptor is not involved in dendritic cell-T-cell interaction (i.e. adhesion) and that the anti-DEC-205 antibodies cannot be used to modulate the immune response.
Curtis et al. (1992), as well as in WO 93/01820, describe a non-CD4 gp120 receptor isolated and cloned from human placenta tissue. This gp120 receptor is expressed on mammalian cells which do not exhibit high levels of CD4, such as placenta, skeleton muscle, brain, neural and mucosal cells, as well as other tissues and cells including colon, thymus, heart, T cells, B cells and macrophages (but not in the liver or the kidney). The amino acid sequence of the C-type lectin gp120 receptor disclosed in SEQ ID NOs:1 and 2 of WO 93/01820 has a high degree of sequence homology (>98%) with the C-type lectins that were found to be present on dendritic cells (WO 00/63251; Geijtenbeek et al., 2000a).
Curtis et al. (1992) and WO 93/01820 further discuss the role this C-type lectin receptor plays in the infection of the aforementioned cells/tissues with HIV, i.e. by binding the major HIV envelope glycoprotein gp120 prior to internalization of the virion into the cell. It was found that inhibition of the C-type lectin gp120 receptor could reduce or inhibit HIV infection of these cells/tissues. As suitable inhibitors, WO 93/01820 discloses mannose carbohydrates, fucose carbohydrates, plant lectins such as concanavalin A, specific antibiotics such as pradimicin A, and sugars such as N-acetyl-D-glucosamine and galactose (which however are described as less potent). These compounds and compositions containing them are used either in vitro or in vivo to inhibit the binding of HIV to the cell surface.
Neither Curtis et al. (1992) nor WO 93/01820 mentions or suggests the presence of a C-type lectin on dendritic cells, nor do these references mention or suggest their role in dendritic cell—T cell interaction during the initial stages of an immune response nor do they mention or suggest that the C-type lectin binds to any yeast or fungi or specifically to C. albicans. 
WO 95/32734 describes FcγRII (CD32) bridging (or crosslinking) compositions and their use in modulating the immune response to specific antigens. This reference is based upon the finding that the bridging of FcγRII (CD32) molecules on antigen presenting cells (APCs) impairs the expression of the essential co-stimulatory molecules B7½ (i.e. prevents their up-regulation) and thereby impairs the expression of (i.e. causes the down-modulation of) the adhesion molecule ICAM-3, with the functional consequence of an impaired capacity of the monocytes to co-stimulate the activation of antigen-specific T cells (i.e. resulting in the modulation of antigen-specific T cell unresponsiveness). The bridging agent is chosen from aggregated human IgG molecules or Fc-fragments thereof; bi- or multivalent monoclonal antibodies to FcγRII or fragments thereof, or a fusion of two or more human IgG Fc parts.
WO 95/32734 is therefore directed towards modulating (i.e. inhibiting) the co-stimulation signal required for T cell activation (i.e. besides the primary signal of TCR/CD3 interaction), in particular to induce proliferation and maturation into effector cells. WO 95/32734 is not directed towards modulating dendritic cell—yeast cell interaction.
WO 98/02456 discloses a group II human C-type lectin isolated from a stimulated human macrophage library. WO 98/49306 discloses a group IV C-type lectin present in human pancreatitis-associated protein (“PAP”). WO 98/41633 discloses a group V human C-type lectin isolated from a human tumor clone.
WO 98/02456, WO 98/49306 and WO 98/41633 further disclose methods for producing antibodies against these C-type lectins. However, none of these references relates to interaction between C-type lectins and yeast.
Dendritic cells (DC) are antigen-presenting cells that capture antigens in the peripheral tissues and migrate via lymph or blood to the T cell area of draining lymph nodes and spleen. Here they present processed antigens to naive T cells, initiating antigen-specific primary T cell responses.
DC are unique in their ability to interact with and activate resting T cells. However, prior to publication of WO 00/63251 and Geijtenbeek et al. (2000a), it was largely unknown how DC-T cell contact is initiated and regulated. Therein, the role of ICAM-3 in DC-T cell interactions was investigated. It was demonstrated that although DC strongly adhere to ICAM-3, this adhesion is not mediated by LFA-1, αD or any other integrin. In the search for this novel ICAM-3 receptor on DC, a C-type lectin receptor, designated DC-SIGN, which is preferentially expressed by DC was cloned. Besides its prominent role in DC-T cell clustering and initiation of T cell responses, it was discovered that DC-SIGN is a major HIV-1 receptor involved in infection of DC and subsequent HIV-1 transmission to T cells. Thus HIV-1 and resting T cells exploit a similar highly expressed receptor to interact with DC.
The publications and other materials used herein to illuminate the background of the invention, and in particular, cases to provide additional details respecting the practice, are incorporated herein by reference, and for convenience, are referenced by author and date in the text and respectively grouped in the appended List of References.